800 V / 12 A RMS SCR in TO-220 — motor drive and power control workhorse
The STMicroelectronics TYN812RG is a standard-recovery SCR (silicon-controlled rectifier) rated for 800 V off-state blocking and 12 A RMS on-state current, housed in a TO-220-3 through-hole package. It is designed for medium-power phase-control applications such as motor speed drives, solid-state relays, heater control, and AC power switching in industrial and appliance environments. With a 15 mA maximum gate trigger current and 1.3 V maximum gate trigger voltage, the TYN812RG can be driven directly by standard optocouplers or low-power logic outputs without an intermediate driver stage, simplifying the gate drive circuit.
Current ratings and surge capability — sizing the load and the protection
The 12 A RMS on-state current (8 A average) sets the continuous load the SCR can carry in a typical 50/60 Hz phase-control circuit. For a resistive heater drawing 10 A RMS, this part provides headroom; for an inductive motor load, derate per the datasheet's temperature curve. The non-repetitive surge current rating of 145 A at 60 Hz (140 A at 50 Hz) covers inrush events such as motor starting or capacitor bank charging — the SCR survives the surge without damage, provided the junction temperature stays within limits. The 30 mA maximum holding current means the SCR latches on once triggered and stays conducting until the load current drops below that threshold — typical for AC line applications where the current crosses zero each half-cycle.
Temperature range and thermal environment
The TO-220 case with a heatsink is the expected mounting — the tab is the anode terminal, so the heatsink must be electrically isolated or at anode potential. The 5 µA maximum off-state leakage at rated voltage is negligible in most designs, but rises with junction temperature — budget for increased leakage above 100°C when sizing the snubber or gate drive.
Because the part is active and widely used, it is available through multiple distribution channels.